1. Field of the Invention
This invention is related to transducers and transducer related systems and in particular to optical encoder motion transducers and systems.
2. Discussion of the Prior Art
Motion transducers are well known in the prior art. These transducers include electromagnetic transducers such as synchros and resolvers, contact transducers such as brush-type encoders, magnetic transducers such as magnetic type encoders, optical transducers such as optical type encoders and optical-type incremental pickoffs, and other such position transducers. Many other motion transducer types are available including tachometers and position switches. Such motion transducers have been incorporated into systems such as digital readout systems, machine control systems, and multitudes of other such systems.
Motion transducers are conventionally used to provide feedback signal for control systems. Many motion transducers are analog transducers such as resolvers, synchros, and tachometers. Digital absolute encoders provide a digital number that defines transducer position and therefore machine position. This digital number, used for control system feedback, can be used for digital control systems operation. Encoders have been implemented as contact, magnetic, or optical encoders. Contact and magnetic encoders have disadvantages such as environmental limitations and wearout. Optical encoders generally provide an improved digital motion transducer. Optical encoders generate a digital output word that is indicative of a shaft position input. They can be used in many applications such as interfacing a computer to a machine, where the encoder can provide a digital number defining the machine's position. Encoders can be used in aircraft, machine tool, position readout, and other systems
Conventional encoders may be characterized by a performance/price/size figure-of-merit. For example, an eight-bit resolution encoder may cost $300, a 14-bit resolution encoder may cost $1,200; and a 24-bit resolution encoder may cost $150,000. The $1,200 14-bit resolution encoder may have a six-inch diameter. A smaller 21/2 inch diameter 14-bit encoder may be available, but for an increased cost of over $2,000. Therefore, conventional encoders have a performance/price/size figure-of-merit; where cost increases rapidly with increased performance and reduced size.
The optical motion transducer field will now be discussed. Prior art optical transducers include optical encoder transducers and optical incremental transducers. Optical encoders conventionally utilize a code wheel with binary-weighted patterns. These patterns are illuminated and sensed with discrete photo-sensors to provide an encoded output of transducer position. Incremental pickoffs provide for chopping of illumination from an illunnation source and sensing the chopped illumination with a discrete photoelectric sensor. An optisyn incremental pickoff utilizes an optical Moire fringe effect to provide an optical rotation that is more rapid than the mechanical rotation; where discrete photosensors mounted in physical quadrature positions detect the optical pattern rotation and derive direction from the sequence of quadrature sensors.
Although the motion transducer art is highly developed, it is characterized by transducers that are relatively high in cost, low in accuracy, and large in size. Such transducers have a figure-of-merit that is related to price, accuracy, and size; where greater precision can be achieved at higher cost and larger size, smaller size can be achieved at higher cost and lower precision, and other such combinations of these three parameters can be provided as compromises or tradeoffs to optimize a transducer for a particular application.
The prior art is represented in the art of record herein.